A glass-ceramic is provided having a thermal expansion coefficient in a range of 4.0 to 8.5 ppm/.degree. C., a dielectric constant in a range of 5 7 and a Quality factor Q of at least 400. The glass-ceramic consists essentially of SiO.sub.2 in a range of 40 55 wt %, Al.sub.2O.sub.3 in a range of 7 22 wt %, MgO in a range of 6 to less than 26 wt %, and at least one of BaO in an amount up to 35 wt %, SrO in an amount up to 37 wt % and ZnO in an amount up to 17 wt %. An electronic package is also provided, including one of a metal and sintered ceramic base member and a glass-ceramic substrate bonded to the base member.