A glass ceramic is specified, with a crystalline phase consisting predominantly of BPO4, and preferably exclusively of BPO4. The glass ceramic contains 10 to 50 wt.-% SiO2, 5 to 40 B2O3, 25 to 75 wt.-% P2O5, up to 5 wt.-% refining agents, up to 1 wt.-% impurities, and 0.1 to 10 wt.-% of at least one constituent selected from the group of M32O3, M52O5 and M4O2, wherein M3 is an element selected from the group of the lanthanoids, yttrium, iron, aluminum, gallium, indium and thallium; wherein M5 is an element selected from the group of vanadium, niobium and tantalum and wherein M4 is an element selected from the group of titanium, zirconium, hafnium and cerium. The glass ceramic is advantageously suitable for being coated with semiconductor materials.