[en] Electron temperature profiles and heat waves at densities above the ECE cutoff are measured at the W7-AS stellarator by a novel diagnostic based on black body emission and Bernstein-extraordinary-ordinary mode conversion of electron Bernstein waves (EBWs). In conclusion, ECE radiometry of overdense plasmas was demonstrated by considering - rather than ordinary (O) or extraordinary (X) mode emission perpendicular to the magnetic field - the black body emission of electron Bernstein (B) waves (EBWs) escaping the plasma along a special oblique line of sight, after B-X-O mode conversion. The original aspects of such approach, compared to traditional ECE, are: 1. the antenna optimization with respect to transmissivity through the cutoff layer and with respect to the Doppler deformation of the spectrum; 2. the broadband phase-shifter, for modal purity of measurements along the oblique line of sight; 3. the mode-converted EBW ray tracing code in 3D hot plasma for profile recovery from spectra. Temperature profiles at high density (up to n_e = 3.8 · 10²⁰ m^-3) and diagnostic applications over time scales faster than those of Thomson scattering (as fast as 1 μs) have been presented. Moreover, for the first time the heat waves method has been extended beyond the ECE cutoff density combining EBW emission measurements at the first harmonic (f = 63-78 GHz) with modulated EBW heating at the second harmonic (140 GHz). (authors)