A large use of silicon microstrip detectors is foreseen for the intermediate part of the CMS tracker. A specific research and development program has been carried out with the aim of finding design layouts and technological solutions for allowing silicon microstrip detectors to be reliably used on a high radiation level environment. As a result of this work single sided, AC-coupled, polysilicon biased, 300 mu m thick, p(+) on n substrate detectors were chosen. Irradiation tests have been performed on prototypes up to fluence 2 x 10(14) n/cm(2). The detector performances do not significantly change if the detectors are biased well above the depletion voltage. S/N is reduced by less than 20%, still enough to insure a good efficiency and space resolution. Multiguard structures has been developed in order to reach high voltage operation (above 500 V).