Realization of low-cost and reliable packaging techniques to couple the optical fiber with the photodetector has become a critical area of research today. In the present work, we have developed a simple technique to automatically align the fiber with the detector by micromachining the InP substrate (used for fabricating the p-i-n detector) and using the resulting V-groove for accurate positioning of the fiber. A masking material has been deposited on the back surface of the wafer and patterned by photolithography to open a window exactly aligned to the p-i-n detector realized on the top surface. InP has been etched anisotropically through this window to a depth of more than 350 mum. This has resulted in a V-groove through which the fiber has been inserted and held in position. Three different etch mask materials viz. Ti, Cr, and SiN have been tried and their suitability to withstand such long time etching has been investigated. HCl:H3PO4 and HBr:CH3COOH etch solutions have been used to etch InP. It has been found that while the choice of the etching solution determines the angle of the V-groove as well as the surface finish, the mask material dictates the amount of undercut. Ti as the mask material with HBr:CH,COOH etch solution has been found to give the best results for this particular application.