A gas distributor for a CVD or OVPD reactor comprises two or more gas volumes (1, 2) into each of which opens a feed pipe (3, 4) for a process gas, each gas volume (1, 2) being connected to a plurality of corresponding process gas outlets (6, 7) which open into the bottom (5) of the gas distributor. In order to increase the homogeneity of the gas composition, the two gas volumes (1, 2) comprise pre-chambers (10, 10′, 11) located in a first common plane (8) and a plurality of gas distribution chambers (12, 13) each associated with a gas volume are provided in a second plane (9′) adjacent to the bottom of the gas distributor. The pre-chambers (10, 10′, 11) and gas distribution chambers (12, 13) associated with each gas volume (1, 2) are connected with connection channels (14, 15).