The diffusion profile of a single drift region (SDR) p+nn+ silicon IMPATT diode is simulated using simple, generalized, and accurate computer methods for dc and small signal analysis of the diode for realizing high negative resistance and conversion efficiency at X‐band (8 to 12 GHz). The results show that the optimized diffusion profile provides a junction depth of 0.83 to 0.86 μm with a surface concentration of 7.5 × 1025 to 1026 m−3. The optimized diode has a narrow avalanche zone with breakdown voltage of 89.3 V and conversion efficiency of 11%. The negative resistance and the negative conductance of the diode are also considerably enhanced due to optimization of the diffusion profile. Copyright © 1992 WILEY‐VCH Verlag GmbH & Co. KGaA