Samples of phosphorus silicate glass (PSG) layers were deposited in a class 100 clean room in two kinds of industrial type reactors: by plasma enhanced chemical vapour deposition (PECVD) and micro pressure chemical vapour deposition (μPCVD) at working temperatures of 380 °C and 430 °C, respectively. After deposition the samples were subjected to rapid thermal annealing (RTA) in a vacuum at 5×10 −3 Pa and temperatures of 800 °C, 1000 °C, 1200 °C and 1400 °C for 15–180 s. X-Ray photoelectron spectroscopy (XPS) investigations show that phosphorous oxides pass through a phase transition and evaporate, while silicon oxides evaporate and decompose. The rate of etching in ‘p’ etcher of μPCVD-PSG layer before annealing is 1023 Å min −1, after RTA at 800 °C for 15 s it is 909 Å min −1, and after annealing for 3 min it is 690 Å min −1. In the case of RTA at 1000, 1200 and 1400 °C for 3 min the etching rates are 660, 469 and 351 Å min −1, respectively, i.e. RTA results in considerable decrease of rate of etching. The same behaviour shows curves related to PSG layers obtained by PECVD. IR spectra show that PO bond vibration at 1320 cm −1 appears at temperatures of annealing T≥1000 °C and time interval 60–180 s. A correlation between PSG layers characteristics and conditions of RTA is found.