Abstract : The CMS (Compact Muon Solenoid) experiment foresaw the use of MSGCs (MicroStrip Gas Chambers) on a surface of about 200 m2 in its inner tracker. The condition of exploitation (luminosity = 10^34 cm-2.s-1) has led to a thorough study of the radiation hardness and long term stability of the MSGCs. For that purpose, the CMS Tracker group of Lyon has proposed and evaluated a variant of MSGC : the SGC (Small Gap Chambers). In order to study the radiation hardness of SGCs, several tests have been done with a pion beam of 350 MeV at the Paul Scherrer Institut in Zurich. Initially performed with small size chambers (5 cm x 2.5 cm), the measured spark rate and the extrapolation to 500 LHC equivalent days led to validate the good hardness of the detectors to LHC intensity. Large size detectors (14 cm x 5 cm) were then tested. A preamplification stage, the GEM (Gas Electron Multiplier) has been added to compensate the increase of the noise and the strip capacitance. The GEM led to a significant decrease of the spark rate and an improvement of the gain margin. The long term ageing study of SGCs was performed with a 55Fe X-ray source of 6.4 keV during several months. The gain loss was estimated by the variation of the current, measured as a function of the integrated charge per centimeter of strip. The results show a loss of about 25% in 5 years of LHC operation at high intensity. The track electron reconstruction in the CMS tracker is important because elec- trons are involved in signature of several physics signals. A study has been done on the improvement of the reconstruction efficiency by introducing an energy loss of the electrons by Bremsstrahlung.