A rewriteable nonvolatile memory cell having two bits per cell is described. The memory cell preferably operates by storing charge in a dielectric charge storage layer or in electrically isolated conductive nanocrystals by a channel hot electron injection method. In preferred embodiments the channel region has a corrugated shape, providing additional isolation between the two storage regions. The channel region is deposited and is preferably formed of polycrystalline germanium or silicon-germanium. The memory cell of the present invention can be formed in memory arrays; in preferred embodiments, multiple memory levels are formed stacked above a single substrate.