The fabrication of microstructure with high aspect ratio is one of the most important issues in MEMS technology. This paper presents a technology of micromachining using electrochemical etching in hydrofluoric acid. Pores with high aspect ratio (>10:1) and smooth surface have been produced in the current study. The dimensions and shapes of etching pores can be varied over a wide range by adjusting electrochemical etching parameters. HF concentration is one of the most important parameter, since it influences not only etching rate but also diameter and the inner surface roughness of pores. The etching rate increases with HF concentration and so does the diameter of pores. Therefore an optimal HF concentration can be obtained. Besides, the inner surface roughness (Ra about 12nm) in 6.1% HF concentration is obtained. The roughness of different pores surface from electrochemical etching and inductively coupled plasma (ICP) etching is also compared. It is observed that pores fabricated by electrochemical etching has relatively smoother surface.