Optically absorbing deposits have been detected by Raman scattering in native oxides on In0.76Ga0.24As0.56P0.44which were formed by thermal oxidation or by annealing electrochemically anodized films. For air oxidation at 560 °C, the Raman line shape of the absorbing deposit could represent either a two phase mixture of As and an alloy of AsxP1−xwithx∼0.7 or pure AsxP1−xwith a somewhat larger value ofx. The latter possibility seems the more likely at this time. Analysis of the Raman band shapes for air oxidation at 730 °C suggests a mixture of two immiscible AsxP1−xsolid solutions, both withx≥0.7. In no case is a simple two phase mixture of crystalline elemental arsenic and red phosphorus detected. Oxidation of the quaternary in As2O3leads to the detection of hexagonal elemental As, AsxP1−x(x>0.7), and InPO4. The detection of InPO4provides an explanation of why the detected AsxP1−xalloys are phosphorus depleted relative to the bulk substrate composition, i.e., the formation of orthophosphates such as InPO4and GaPO4deplete the potential source of elemental phosphorus. No absorbing deposits were detected in as‐grown anodic films on the quaternary, but annealing the anodic films leads to the formation of an optically absorbing layer. The Raman band shape associated with this deposit is broad and has been tentatively assigned as an AsxP1−xalloy. There is insufficient structure, however, to provide an accurate estimate ofxor to exclude the possibility that it contains some admixture of amorphous arsenic.