A thermostat for cooking appliances powered by gas includes a body defining an inlet conduit and an outlet conduit that receive a gas flow from a supply source and to supply it to a gas burner, and a chamber having a substantially cylindrical shape that is in fluid communication with the inlet conduit, and also with the outlet conduit either directly, through a main opening formed at one end thereof, or indirectly, through a secondary conduit formed in the body of the thermostat. The gas flows into the outlet conduit bypassing the main opening. A one-piece valve adjusting the gas flow rate is coaxially fitted in the chamber and guided by its peripheral walls. These features make the structural configuration of the thermostat body and its conduits is much more compact, functional and less expensive than in thermostats known in the art.