Two distinct processes are suggested for the formation of p‐n junctions in crystal platelets of GaP grown from Ga solution doped with Zn, Te, and O, over wide ranges of composition and growth conditions. In each growth melt, about one half of the p‐type crystals contain a shallow n‐type surface layer, ∼2 μ in thickness, formed by out‐diffusion of Zn after growth. These p‐n junctions have relatively high (≫10-3) external electroluminescence quantum efficiencies at room temperature. The remaining p‐type crystals contain deeper, less efficient junctions, built into the crystals by impurity segregation effects during growth. The efficiencies of p‐n junctions degrade with the heat treatment at 600°C used to alloy the Ohmic contacts. The extent of degradation correlates with the dislocation density and is ascribed to precipitation. The precipitates nucleate preferentially in the junction plane and grow with subsequent heat treatment.