The effects of microwave interference on the operational parameters of individual MOSFET devices on CMOS wafers were studied as microwave power and frequency were varied. The study used direct injection of microwave power into the device terminals, and the output characteristics were measured with and without the microwave interference. The study showed that injected microwave power significantly affects output current, transconductance, output conductance, and breakdown voltage for power levels above 10 dBm in the frequency range between I and 20 GHz. The effects result in the devices loosing switching-off capability, saturation and linearity in the amplification region of their output characteristics, and developing DC offset currents at zero drain bias, while breakdown shifts to significantly lower voltages. Most importantly the sensitivity to microwave power was strongly suppressed at frequencies above 5 GHz indicating the possibility of a by-pass path for the injected power through intrinsic capacitive coupling of the devices to ground. (C) 2004 Elsevier Ltd. All rights reserved.