A semiconductor manufacturing method and apparatus is provided that can improve uniformity of processing time of oxidation thickness. When starting a heat oxidation process, a time for optimum oxidation processing in the process management system is calculated based on atmospheric pressure data, a target thickness of that process, oxidization time, thickness data and atmospheric pressure data in the immediately preceding process under the same oxidization processing job. The optimum system comprises a process management system such as a host computer, a device having a barometer, a heat oxidation-processing device and a thickness-measuring device. The host computer, the barometer, the heat oxidation processing device and the thickness-measuring device are connected via a network so as to transmit data to and from each device.