A semiconductor manufacturing apparatus and a wafer loading/unloading method thereof increase productivity. The semiconductor manufacturing apparatus includes a first boat and a second boat having a plurality of first slots and a plurality of second slots, respectively, and disposed such that the first slots and the second slots alternate each other, the first boat mounting a plurality of first wafers in the first slots to direct front faces of the first wafers in a predetermined direction, the second boat mounting a plurality of second wafers in the second slots to direct back faces of the second wafers in the predetermined direction; a reaction tube having an opening and containing the first and second boats mounting the first and second wafers; a plate sealing up the opening of the reaction tube containing the first boat and the second boat; a reaction gas supplier supplying reaction gas into the sealed reaction tube for a predetermined process; and a reaction gas exhauster exhausting the reaction gas from the reaction tube to the external of the reaction tube after the predetermined process.