The bonding chemistry of various GaAs-to-oxide/GaAs bonded samples was investigated using multiple internal transmission Fourier transform infrared spectroscopy for thermally annealed and thermocompression annealed samples. The oxides used in these investigations included a native GaAs oxide as well as two compositions of borosilicate glass ͑BSG͒ deposited by low-pressure chemical vapor deposition ͑LPCVD͒. For the thermally annealed samples, the hydrogen-bonded H 2 O/OH groups on the hydrophilic surface form a room temperature bond without the application of pressure. Chemical changes at the wafer-bonded interface occur in two temperature regions. For anneals between 200 and 400°C for 1 h in N 2 , the H 2 O/OH groups react and evolve H that becomes absorbed within the oxide. The LPCVD BSG oxide was chemically unaltered during anneals in this temperature range, however, the GaAs native oxide underwent chemical modification. Initially, the GaAs oxide consisted of As͑III͒-O and Ga-O related oxides. The As͑III͒-O oxides react to form free As and Ga-O during annealing between 200 and 400°C. For anneals between 500 and 600°C, the reaction of H 2 O/OH groups continue and the H becomes infrared inactive, most likely forming H 2 voids at the bonded interface. In addition, As͑V͒-O related oxides were observed during thermal annealing in this temperature range. No detectable chemical changes in the BSG were observed over the temperature range investigated. Samples that were annealed under an estimated 1-10 MPa of pressure had similar chemical changes to thermally annealed samples.