[en] Standard 1. and 2. harmonic ECRH at 70 GHz and 140 GHz fails to support high-density operation >10²⁰ m^-3, which is necessary to attain detachment at W7-AS island divertor configuration. ECRH is limited by the O1-cutoff (0.6 x 10²⁰ m^-3) for 70 GHz and the X2-cutoff (1.2 x 10²⁰ m^-3) for 140 GHz respectively at 2.5 T. For the propagation of electron Bernstein waves (EBW), however, no upper density limits exist, but they have to be generated by the OXB-mode conversion process from the electromagnetic waves. For this process threshold densities of 0.6 x 10²⁰ m^-3 (70 GHz) and 2.4 10²⁰ m^-3 (140 GHz) exist. Efficient OXB heating with 70 GHz has already been successfully demonstrated at Wendelstein 7-AS, but the higher harmonic OXB heating with 140 GHz EBW's remained unexplored until improved performance by divertor operation above the critical density of 2.4 x 10²⁰ m^-3 was shown recently. Complementary to EBW-heating, an EBW emission diagnostic was developed to measure temperature profiles with a high temporal resolution at high densities inaccessible for the standard ECE. This diagnostic, which is called EBE (Electron Bernstein wave Emission), makes use of the inverse OXB-process and the black body cyclotron emission of the EBW's. With the help a 3D ray-tracing code the temperature profile can be reconstructed from the emission spectrum. Successfully heating of extreme high-density plasma, which are achievable now for divertor operation at Wendelstein 7-AS, was demonstrated with 140 GHz second, third and fourth harmonic electron Bernstein waves. This ECRH frequency is foreseen for the large Wendelstein 7-X experiment, which is in construction now. The reason for the high OXB-mode conversion efficiency is mainly the extremely steep density gradient in the high-density target plasma at Wendelstein 7-AS. Further, current drive with the 70 GHz first harmonic Bernstein waves was demonstrated for the first time. (authors)