  We study the compressible states in the quantum Hall system using a mean
field theory on the von Neumann lattice. In the lowest Landau level, a kinetic
energy is generated dynamically from Coulomb interaction. The compressibility
of the state is calculated as a function of the filling factor $\nu$ and the
width $d$ of the spacer between the charge carrier layer and dopants. The
compressibility becomes negative below a critical value of $d$ and the state
becomes unstable at $\nu=1/2$. Within a finite range around $\nu=1/2$, the
stable compressible state exists above the critical value of $d$.
