Porous silicon structures were observed in laser-assisted etching in a TMAH solution. The porous structures significantly increase the active surface areas and therefore are of great interest to the pharmaceutical and fine chemicals industry, in the areas of high throughput drug discovery, reaction optimization and process development. Laser-assisted etching of silicon using a Nd:YAG laser with a TMAH solution is rarely studied but desirable as the solution is nontoxic. To the best of our knowledge, the porous structures directly produced this way have not been reported previously. In this paper, we discuss our experimental results and the possible mechanism of formation of the porous structures. A dummy micro-reactor was fabricated with selective porous surface structures to demonstrate its potential industrial applications.