The thermal sensitivity of the efficient type II angular phase matching configuration for frequency doubling in 2‐amino‐5‐nitropyridinium‐dihydrogen crystals has been measured accurately. The measured thermo‐optic tuning sensitivity was found to be −0.303 mrad/ °C. A wavelength shift of the noncritical phase‐matching angle resulting from the thermal effect is shown to correspond to ad&lgr;/dTcoefficient of 0.176 nm/ °C. ©1995 American Institute of Physics.