This letter describes the design and fabrication of a high-linearity GaN PIN MMIC switch. In order to achieve good input/output matching and high-linearity characteristics at the K-band, a GaN PIN-diode-based switch was employed with an absorptive-type topology. The fabricated GaN PIN MMIC switch demonstrated good performance characteristics such as input/output return losses of higher than 10.5 dB and a high IIP3 of 52.0 dBm. To our knowledge, this is the first GaN PIN-diode based MMIC switch demonstrated up to the K-band.