A substrate processing device contains a substrate loading/unloading area for loading/unloading of substrates. The substrate processing device further has a process chamber, a carrier device with which the substrates are transported by a carrier transport device to the process chamber, and a gas-tight closing device between the process chamber and the carrier transport area as well as a gas-tight closing device between the substrate loading/unloading area and the carrier transport area. The substrate processing device allows substrate processing at a high quality with high process purity, thereby being suitable for mass production. The object is achieved by the substrate loading/unloading area being coupled with the carrier transport area by a substrate transfer area with a substrate transfer device for transferring the substrates from a substrate cassette provided in the substrate loading/unloading area and in which substrates can be arranged in different horizontal cassette levels of the substrate cassette.