Spray coating of a photoresist onto three-dimensional (3D) structure was investigated. To improve the uniformity of photoresist deposition onto the 3D structure, a shield plate with an aperture was used. The shield plate set over a sample permitted the resist deposition on the sample surface located in the aperture area while the plate blocked the deposition for the other area. The spray flow which is suitable for the resist deposition can be used effectively. Numerical analysis revealed that the vertical velocity component of gas flow was enhanced in the aperture area. In the experiments of the spray coating, the difference between the resist film thicknesses deposited on top and bottom trench surfaces was decreased. On the trench sidewall, resist bump formation, which was frequently observed in spray coating, was suppressed. The uniform resist deposition is necessary to realize 3D microdevices by lithography. In the microfluidic devices of dielectrophoresis, aside from the top and botttom trench surfaces, the trench sidewall can be used to fabricate device structures such as electrode for dielectrophoresis.