A gas supply system adapted to provide alternating deposition or etching gases to a process chamber used to manufacture semiconductors, said gas supply system comprising: a first and a second mass flow controller (11, 13); a first and a second gas bypass (16, 18); the system being arranged such that in operation a first gas is provided to the first mass flow controller, the first gas either being an etchant gas (10, 12) or a deposition gas; and such that a second gas is provided to the second mass flow controller, the second gas either being an etchant gas or a deposition gas; an exhaust suitable for being in fluid communication with a chamber exhaust; a first gas line in fluid communication with the first mass flow controller, a first gas chamber inlet valve and a first gas chamber bypass valve, the first gas chamber bypass valve in fluid communication with the first mass flow controller and the exhaust by the first gas bypass; a second gas line in fluid communication with the second mass flow controller, a second gas chamber inlet valve and a second gas chamber bypass valve, the second gas chamber bypass valve in fluid communication with the second mass flow controller and the exhaust by the second gas bypass; the first gas chamber inlet valve, the first gas chamber bypass valve, the second gas chamber inlet valve and the second gas chamber bypass valve form a discrete gas switch; wherein in use the discrete gas switch is configured such that the first gas is directed to the process chamber through the first gas line by opening the first gas chamber inlet valve and closing the first gas chamber bypass valve while at the same time the second gas is directed straight to the exhaust by closing the second gas chamber inlet valve and opening the second gas chamber bypass valve; and such that the second gas is directed to the process chamber by opening the second gas chamber inlet valve and closing the second gas chamber bypass valve while at the same time the first gas is directed straight to the exhaust by closing the first gas chamber inlet valve and opening the first gas chamber bypass valve; and such that the flow of deposition or etchant gas (10, 12) from said first mass flow controller and the flow of deposition or etchant gas (10, 12) from said second mass flow controller is alternatively switched such that the flow of deposition or etchant gas (10, 12) from said first mass flow controller and the flow of deposition or etchant gas from said second mass flow controller to said process chamber remains at a specified process setpoint value. a first and a second mass flow controller (11, 13); a first and a second gas bypass (16, 18); the system being arranged such that in operation a first gas is provided to the first mass flow controller, the first gas either being an etchant gas (10, 12) or a deposition gas; and such that a second gas is provided to the second mass flow controller, the second gas either being an etchant gas or a deposition gas; an exhaust suitable for being in fluid communication with a chamber exhaust; a first gas line in fluid communication with the first mass flow controller, a first gas chamber inlet valve and a first gas chamber bypass valve, the first gas chamber bypass valve in fluid communication with the first mass flow controller and the exhaust by the first gas bypass; a second gas line in fluid communication with the second mass flow controller, a second gas chamber inlet valve and a second gas chamber bypass valve, the second gas chamber bypass valve in fluid communication with the second mass flow controller and the exhaust by the second gas bypass; the first gas chamber inlet valve, the first gas chamber bypass valve, the second gas chamber inlet valve and the second gas chamber bypass valve form a discrete gas switch; wherein in use the discrete gas switch is configured such that the first gas is directed to the process chamber through the first gas line by opening the first gas chamber inlet valve and closing the first gas chamber bypass valve while at the same time the second gas is directed straight to the exhaust by closing the second gas chamber inlet valve and opening the second gas chamber bypass valve; and such that the second gas is directed to the process chamber by opening the second gas chamber inlet valve and closing the second gas chamber bypass valve while at the same time the first gas is directed straight to the exhaust by closing the first gas chamber inlet valve and opening the first gas chamber bypass valve; and such that the flow of deposition or etchant gas (10, 12) from said first mass flow controller and the flow of deposition or etchant gas (10, 12) from said second mass flow controller is alternatively switched such that the flow of deposition or etchant gas (10, 12) from said first mass flow controller and the flow of deposition or etchant gas from said second mass flow controller to said process chamber remains at a specified process setpoint value.