Colonoscopy is an important procedure for the diagnosis of various pathologies, in particular cancer of the colon and of the rectum, the second most malignant tumor in industrialized countries. At present however, colonoscopy is a procedure often painful for the patient and complex for the doctor. This is mainly due to the characteristics of current colonoscopes, which are quite rigid and require the doctor to perform difficult maneuvers for insertion. In this paper we present the concept and describe the design and fabrication of a new system for colonoscopy based on a microrobot capable of being propelled semi-autonomously along the colon. The microrobot system comprises a mothership incorporating devices for clamping the colon wall and tools for diagnosis and intervention. The actuation system is based on purposely developed shape memory alloy (SMA) pneumatic microvalves. A human/machine interface allows the doctor to teleoperate or supervise the functioning of the microrobot and to receive visual and other information during endoscopy. Particular attention has been paid to investigating a reliable and safe method of locomotion and to develop an efficient clamping system for the microrobot. The resulting configuration of the microrobot is very simple and potentially suitable for real clinical application. A prototype microrobot system has been tested in vitro with promising results.