Impedance and microwave reflectivity measurements for n-Si(100) and (111) in 1M LiCl/methanol are presented. The silicon surface seems to be unstable, probably as the result of slow oxidation, but reasonably stable conditions were established after several hours. The microwave reflectivity/potential curves for different modulation frequencies have been fitted satisfactorily by a simple model. The flatband potentials obtained from single-frequency microwave measurements were -755 mV for the (100) and -617 mV for the (111) surface vs. a silver reference electrode. The changes in microwave reflectivity provide definitive evidence for the formation of an inversion layer under higher reverse bias. The time constant for formation of the inversion layer was in the range 0.1 to 0.3 a. An order of magnitude reduction of the hole mobility within the inversion layer was observed, with values falling to 30 cm(2)V(-1)s(-1). Separation of the currents charging the inversion layer, the space-charge capacitance, and surface states was achieved by measuring induced changes of the. conductivity via the microwave reflectivity. The Helmholtz capacitance derived by deconvolution of the response was approximately 5 mu F cm(-2).