A solid state 9.4 GHz microwave refractometer has been developed using a new technique for phase measurement. Noise level in a passband of 0.3 to 30 Hz is about 0.03 N‐unit rms using a 10 mW microwave source with losses of 30 dB between source and sampling cavity. It is easily adapted to measuring multiple sampling cavities simultaneously, thus allowing absolute and relative refractive indices (in various combinations) to be observed at several locations.