A gas gap heat switch has been developed for use in space borne cryogenic systems. The switch is simple, small and lightweight. Due to the absence of moving parts lifetime and reliability are expected to be very high.Four switches have been manufactured and thermal and vibration tests have been successfully carried out. The lowest resonant frequency is 380 Hz and the switches underwent a random vibration up to 11 G in all directions from 30 to 2000 Hz, and a constant acceleration test at 15 G between 15 and 100 Hz.As an example an “on” thermal conductance at 4 K of ≈ 35 mW.K-1 was measured and the on to off ratio was found to be of the order of 2700. The switching temperature is around 15 K.