Piece-like SAPO-34 crystals were directly assembled into a highly oriented seed layer on the α-Al₂O₃ substrate by using spin-coating, and then a preferentially oriented SAPO-34 membrane with no large defects was prepared on an oriented SAPO-34 seed layer by secondary hydrothermal microwave growth. The synthesized membrane exhibited a high CO₂ permeance of 1.57 × 10⁻⁶ s⁻¹ Pa⁻¹ at 302 K and 138 kPa pressure drop, with a CO₂/CH₄ separation selectivity of 109.