  A sigma model action with N=2 D=6 superspace variables is constructed for the
Type II superstring compactified to six curved dimensions with Ramond-Ramond
flux. The action can be quantized since the sigma model is linear when the
six-dimensional spacetime is flat. When the six-dimensional spacetime is
$AdS_3\times S^3$, the action reduces to one found earlier with Vafa and
Witten.
