Most asked topics: PN junction, MOSFET , CMOS, fabrication
Core companies focus on CMOS, power, yield, reliability
Freshers are evaluated on concept clarity + application
Manufacturing companies test process flow and yield
Memorization alone leads to rejection
These are first-round filter questions. If you struggle here, the interview will not go deeper.
What is a semiconductor?
Answer: A semiconductor is a material whose electrical conductivity lies between that of a conductor and an insulator.
Explanation: Its conductivity can be controlled using doping, temperature, light, and electric fields.
Examples: Silicon (Si), Germanium (Ge), Gallium Arsenide (GaAs)
Why is silicon used as a semiconductor material?
- Abundant and low cost
- Moderate band gap (~1.1 eV)
- Forms stable SiO₂ oxide layer (essential for IC fabrication)
- High thermal stability
- Easy to dope
- Offers long device lifetime and reliability
What is intrinsic and extrinsic semiconductor?
Intrinsic Semiconductor: Pure semiconductor, equal electrons and holes, low conductivity (e.g., pure silicon)
Extrinsic Semiconductor: Doped semiconductor, higher conductivity
n-type: Pentavalent dopants (P, As)
p-type: Trivalent dopants (B, Al)
What is doping?
Adding controlled impurities to a pure semiconductor to increase conductivity.
Pentavalent → n-type
Trivalent → p-type
What is a PN junction?
Formed by joining p-type and n-type semiconductors. Basic building block of diodes, transistors, and ICs.
What is the depletion region?
Area near the PN junction where free charge carriers recombine, leaving immobile ions that act as a potential barrier.
What are majority and minority carriers?
Majority carriers: electrons (n-type), holes (p-type)
Minority carriers: holes (n-type), electrons (p-type)
What is band gap energy?
Energy difference between the valence band and conduction band.
Conductors → ~0 eV
Semiconductors → small band gap (Si ≈ 1.1 eV)
Insulators → large band gap
What is recombination and generation?
Recombination: electron + hole → energy released
Generation: energy creates electron-hole pairs
What is Fermi level?
Energy level where the probability of finding an electron is 50% at equilibrium.
Intrinsic → mid-band
n-type → near conduction band
p-type → near valence band
Mentor Tip: If you can’t clearly explain a PN junction, you are not ready for any semiconductor interview.
Difference Between Conductor, Semiconductor, and Insulator
| Property |
Conductor |
Semiconductor |
Insulator |
| Band gap |
~0 eV |
Small |
Large |
| Conductivity |
High |
Moderate |
Very low |
| Temperature effect |
Decreases |
Increases |
No change |
| Examples |
Copper |
Silicon |
Glass |
Forward Bias vs Reverse Bias
| Type |
Effect on Depletion |
Current/Resistance |
| Forward Bias |
Depletion narrows |
Junction conducts, low resistance |
| Reverse Bias |
Depletion widens |
Small leakage, high resistance |
Breakdown Voltage: Minimum reverse voltage at which a diode conducts heavily. Types: Zener, Avalanche.
Drift Current vs Diffusion Current:
| Type |
Driving Force |
Bias Dominance |
| Drift |
Electric field |
Reverse bias |
| Diffusion |
Concentration |
Forward bias |
Other Concepts:
Hall Effect: Identify n/p type, measure carrier concentration and magnetic field
LED and Photodiode: LED (forward biased, emits light), Photodiode (reverse biased, converts light to current)
Rectifier and Ripple Factor: Converts AC to DC; ripple factor indicates DC output quality
Reality Check: 80% of freshers fail because they memorize definitions without understanding working and applications.
Semiconductor Interview Questions for Freshers
Explain the working of a PN junction diode.
What is a BJT? Explain its working and applications.
What is a MOSFET? Explain structure, working, and advantages.
What is CMOS technology? Why is it widely used?
What is the difference between BJT and MOSFET?
What are the applications of MOSFET?
What is VLSI? Explain its importance in semiconductor industry.
What is a rectifier? Explain ripple factor and its significance.
Mentor Tip: For MOSFET, BJT, or CMOS questions, always answer in this order: Structure → Working → Advantages → Applications
Where to find detailed answers: All detailed Answers are available in the Free Semiconductor Interview Questions PDF
Semiconductor Interview Questions for Core Companies
Core semiconductor companies focus on fabrication, CMOS scaling, power, and reliability.
Common Core Company Interview Questions:
Explain the complete CMOS fabrication process step-by-step.
What are short channel effects in MOSFETs?
What is DIBL (Drain Induced Barrier Lowering)?
What is threshold voltage and how does it vary with scaling?
What are leakage currents in CMOS circuits?
Explain static power vs dynamic power dissipation.
What are setup time and hold time in digital circuits?
What is yield in semiconductor manufacturing?
What is latch-up and how can it be prevented?
What is the hot carrier effect?
Core Company Reality: Companies like Samsung, Tata Technologies, Intel, and Qualcomm test CMOS, fabrication, power, and reliability, not just PN junction basics.
Answers to all core-level questions are included in the Free Semiconductor Interview Questions PDF
Samsung Semiconductor Interview Questions (Pattern-Based)
Common Samsung Interview Questions:
Explain CMOS inverter working with voltage transfer characteristics.
What is static power dissipation and dynamic power dissipation?
Explain setup time and hold time.
What is DFT and why is scan chain used?
What is clock skew and how does it affect timing?
What is IR drop in VLSI circuits?
What is crosstalk and how is it reduced?
What are LVS and DRC checks?
What is ESD and how do you protect circuits from it?
Samsung Interview Focus: CMOS fundamentals + STA + DFT basics + fabrication knowledge.
Tata Technologies Semiconductor Interview Questions (Pattern-Based)
Common Tata Technologies Interview Questions:
Explain the complete semiconductor manufacturing flow.
What are the steps involved in wafer fabrication?
Explain thermal oxidation in semiconductor processing.
What is diffusion and ion implantation?
Explain photolithography with masks and photoresist.
What is etching and its types?
Explain metallization in IC fabrication.
What is a cleanroom and why is it important?
What is yield analysis in semiconductor manufacturing?
Tata Interview Focus: Manufacturing processes + yield + quality control.
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