We have observed optical scintillations and corresponding electric current pulses when uniformly heating potassium titanyl phosphate (KTP) crystals at 0.1–0.4 K/s over the temperature range 8–300 K. The scintillations correspond to molecular nitrogen emission occurring during the electrical breakdown of air near the crystal surface, and imply the existence of pyroelectrically induced peak electric fields at the crystal surface exceeding 30 kV/cm, which is ten times larger than dc electric fields reported to induce electrochromic (EC) damage in this material. Recent optical damage studies on KTP under high repetition rate, high average-power laser irradiation reveal an EC-like damage, implying the existence of an internal electric field arising during laser irradiation. Our observation of a sizable total pyroelectric response suggests one possible mechanism for the origin of these internal fields in KTP and other nonlinear optical materials. ©1997 American Institute of Physics.