  The highest critical temperature of superconductivity Tc has been achieved in
cuprates: 133 K at ambient pressure and 164 K at high pressures. As the nature
of superconductivity in these materials is still not disclosed, the prospects
for a higher Tc are not clear. In contrast the Bardeen-Cooper-Schrieffer (BCS)
theory gives a clear guide for achieving high Tc: it should be a favorable
combination of high frequency phonons, strong coupling between electrons and
phonons, and high density of states. These conditions can be fulfilled for
metallic hydrogen and covalent hydrogen dominant compounds. Numerous followed
calculations supported this idea and predicted Tc=100-235 K for many hydrides
but only moderate Tc~17 K has been observed experimentally. Here we found that
sulfur hydride transforms at P~90 GPa to metal and superconductor with Tc
increasing with pressure to 150 K at ~200 GPa. This is in general agreement
with recent calculations of Tc~80 K for H2S. Moreover we found
superconductivity with Tc~190 K in a H2S sample pressurized to P>150 GPa at
T>220 K. This superconductivity likely associates with the dissociation of H2S,
and formation of SHn (n>2) hydrides. We proved occurrence of superconductivity
by the drop of the resistivity at least 50 times lower than the copper
resistivity, the decrease of Tc with magnetic field, and the strong isotope
shift of Tc in D2S which evidences a major role of phonons in the
superconductivity. H2S is a substance with a moderate content of hydrogen
therefore high Tc can be expected in a wide range of hydrogen-contain
materials. Hydrogen atoms seem to be essential to provide the high frequency
modes in the phonon spectrum and the strong electron-phonon coupling.
