The effect of gamma irradiation on MOS devices prepared under different oxidation conditions Is investigated. The C-V characteristics of the devices are studied before and after exposing the latter with gamma radiations of CO60(1.17 and 1.33 MeV gamma rays). For MOS transistor (n-channel depletion type devices) the C-V characteristics change slightly towards the negative voltage axis and the Cminalso decreases after Irradiation. For MOS capacitor (wet oxide) there is a change from high frequency C-V characteristics to low frequency C-V characteristics. In the case of a MOS capacitor (HCl grown) breakdown occurs relatively at lower voltage.