As micromachining in semiconductor materials is known to be precise with micrometre or even submicrometre dimension control, it is well suited for building optical microsystems. In this paper the potentials for microstructure technologies (MSTs) are presented, with focus on optical telecommunication systems. The specific parts and requirements for telecom systems are presented, as well as areas where future MST can be advantageous to use. Our own work at Uppsala University in this field is also presented. It has mainly been focused on how to use MST for passive alignment when building hybrid micro optical systems.