Rendina et al. recently proposed the original configuration of an electromagnetic power sensor for microwaves and millimeter waves that is based on an optically interrogated all-silicon chip [Electron. Lett. 35, 1748 (1999)]. Here we theoretically analyze and discuss in detail the performances of such a new class of nonperturbing and wideband probe in terms of sensitivity, resolution, intrinsic detectivity, linearity, and response time. Good agreement between theory and experiments is demonstrated. In particular, minimum resolutions of approximately 1 mW/cm2 are obtained at frequencies beyond 10 GHz. The dependence of response on the geometrical and electromagnetic parameters of the sensing element is analyzed, and on this basis the possibility of achieving optimized configurations is discussed.