The invention discloses a manufacturing method for flash memories. The method for manufacturing the memory area of a flash memory includes the following steps: step one, forming active areas, and finishing the making of the first gate structures of flash memory cells, wherein the active areas are separated by field oxide formed on the surface of a silicon substrate, and are in bar-shaped structures and in parallel arrangement, and the polycrystalline silicon control gates of the first gate structures in the same row are connected together and form polycrystalline silicon rows; step two, forming an etch barrier layer on the surface of the active areas that are not covered by the polycrystalline silicon rows; step three, performing self-aligned source area field oxide etching, and removing field oxide self-alignment in source area forming areas, etching areas being defined by the polycrystalline silicon rows and silicon self-alignment, and the etch barrier layer preventing the silicon surfaces of the active areas from generating etching during self-aligned source area field oxide etching; and step four, removing the etch barrier layer. The method can prevent the surfaces of the active areas in source areas from generating etching loss and roundness during SAS field oxide etching, and therefore, the performance of devices can be enhanced.