Numerical models of magma emplacement during crustal extension show that shallow (<10 km) rhyolitic to andesitic magma chambers can form and be maintained at typical rates of extension of continental crust. Chambers at depths of 8 km form within 90 ka after emplacement of a total width of 4 km of magma at half extension rates of 2 cm/yr. Once even a small (∼1 km wide) shallow chamber has formed by any process, it can be maintained by extension at a half rate of 1 cm/yr; high temperatures are maintained at a half rate of ∼0.5 cm/yr. Continental rifts and dilational jogs along strike-slip faults in arcs provide areas where extension rates are most appropriate. Large granitoids and batholiths can form by this process over millions of years; actual chambers at any one time may be considerably smaller than preserved granitoids.