Average second‐harmonic power at 5.3 &mgr;m exceeding 0.75 W with a 17% power conversion efficiency has been obtained by pumping a CdGeAs2crystal, cooled to near 77 K, with a Q‐switched CO2laser. Average and peak conversion efficiencies of 21 and 30%, respectively, were achieved at a pulse rate of 1.5 kHz. In cw operation the crystal gave a second‐harmonic output of 73 mW with a conversion efficiency near 0.5%.