We present a new approach for wavefront characterization of near transform-limited intense femtosecond beams using the angular and spectral dependences of the second-harmonic generation conversion efficiency in uniaxial crystals. The method is applied to different aberrated beams and results are compared with the measurements performed with a commercial sensor, finding very good agreement. The phase retrieval dependence with different parameters (e.g. crystal thickness) is discussed. Successful application to sharpen intensity profiles is also demonstrated.