It does not appear to be a valid archive (Byte array to zip file in c#.net)

I am facing issue while converting byte array to zip file.Even though zip file is created using the below code but when I am extracting the zip file I am getting error "Cannot open file. It does not appear to be a valid archive".

private static void ShowZipFile(string fileName, byte[] data)
{
    byte[] compress = Compress(data);
    File.WriteAllBytes(fileName, compress);
}            

private static byte[] Compress(byte[] data)
{
    using (MemoryStream memory = new MemoryStream())
    {
        using (GZipStream gzip = new GZipStream(memory,
        CompressionMode.Compress, true))
        {
            gzip.Write(data, 0, data.Length);
        }
        return memory.ToArray();
    } 

}