The avalanche breakdown of reverse biasedp‐njunctions in GaP is investigated. Electrical studies comprise measurements of I‐V characteristics, breakdown field, and electrical noise as functions of temperature. The high‐temperature light emission from microplasmas consists of a broad emission band with a maximum, near 1.7–1.8 eV, but otherwise with no structure. Its shape is analyzed in detail and discussed in view of theoretical models. The quantum efficiency of this band is independent of the lattice temperature. Neither the spectral shape nor the quantum efficiency of the emission band appear to be related to details of the energy‐band structure. At low temperatures, additional emission lines caused by minority carrier recombination outside the breakdown region are observed.