This paper presents a novel development method for fabricating high aspect ratio microstructures in deep x-ray lithography. In this method, microstructures are developed downward to utilize the difference of the specific weight between the development products and the developer to efficiently remove the development products. The development behaviours of the proposed method (downward-development) are investigated and compared with the conventional method (upward-development). Experimental results indicate that the developing rate of downward-development is approximately twice that obtained by upward-development. Additionally, the development products are easily removed and a satisfactory microstructure quality is achieved via this process. The proposed method also yields accurate predictability to estimate the necessary developing time. Moreover, the elevated temperature increases the developing rate of downward-development more sensitively than for upward-development.