A gas injector may comprise: a gas introduction tube configured to introduce reaction gas into a reaction tube from a gas supply source; and/or a gas distributor connected to the gas introduction tube, extending from the gas introduction tube in a direction within the reaction tube, including a plurality of ejection holes in an inner surface of the gas distributor, and having an arc shape extending in a circumferential direction of the reaction tube. The ejection holes may be spaced apart from each other in the extending direction of the gas distributor, and are configured to spray the reaction gas.