Experimental investigations on detection of terahertz radiation are presented. We used plasma wave instability phenomenon in nanometer Silicon field effect transistor. A 30 nm gate length transistor was illuminated by THz radiation at room temperature. We observe a maximum signal near to the threshold voltage. This result clearly demonstrates the possibility of plasma wave THz operation of these nanometer scale devices. The response was attributed to a non resonant detection. We also demonstrate the possibility to observe a resonant detection on the same devices.