Reactor for producing silicon by chemical vapor deposition, the reactor comprising a reactor body that forms a container, at least one inlet for a silicon-bearing gas, at least one outlet, and at least one heating device as a part of or operatively arranged to the reactor, distinctive in that at least one main part of the reactor, which part is exposed for silicon-bearing gas and which part is heated for deposition of silicon on said part, is produced from silicon. Method for operation of the reactor.