In this paper, two novel concepts that use optically reconfigurable RF circuits are presented. In the first example, a Silicon switch was implemented in the input matching network of a power amplifier. The silicon gap-loaded switch properties were changed from insulator state to near conducting state under illumination and resulted in the change of the effective length of the stub in the input matching network, while the output matching network was not changed. Tunable class AB power amplifier with the optical switch in the input matching circuit has obtained the frequency tuning range of 2.5–3.5 GHz with no significant loss in efficiency and linearity. An optically reconfigurable antenna system (ORAS) could be realized on a single chip using Silicon based technology.