The technique of channel cracking is used to study the crack growth in SiOCH low-k films. Various film thicknesses are produced using consecutive PECVD deposits on silicon substrates in up to the critical thickness for which spontaneous cracks appear. After determining mechanical properties and residual stresses of these films, samples are cleaved, and subjected to four-point bending tests. During the loading in ambient environment, cracks propagate from defects due to cleavage. Propagation of these cracks is observed in situ in order to correlate crack growth velocities to film thickness and total stress in the film. These results allow plotting crack growth rate versus stress intensity factor for crack velocity varying from 10-9 to 10-4 m/s for a stress intensity factor about 0.1 MPa√m. Moreover, in this range of velocities a model is proposed for this material to determine the film stress required to produce channel cracking, for a given film thickness.