Pulse height spectra of Am-241 taken 2-mm CdZnTeSe detector was simulated using Mathematica. In simulation, electronic noise was added in terms of Gaussian white noise (standard variation = 1.5 keV) to reflect detector leakage current and thermal noise of electronic circuit(peramp, read-out circuit etc). Added noise will contribute to FWHM by 3.5 keV (2.355*standard variation of noise). Charge c..