VB.NET Signature:

<DllImport("kernel32.dll", SetLastError:=True)> _
    Public Shared Function WriteProcessMemory(
    ByVal hProcess As IntPtr,
    ByVal lpBaseAddress As IntPtr,
    ByVal lpBuffer As Byte(),
    ByVal nSize As Int32,
    <Out()> ByRef lpNumberOfBytesWritten As IntPtr) As Boolean
    End Function

C# Signature:

[DllImport("kernel32.dll", SetLastError = true)]
  public static extern bool WriteProcessMemory(
  IntPtr hProcess,
  IntPtr lpBaseAddress,
  byte[] lpBuffer,
  Int32 nSize,
  out IntPtr lpNumberOfBytesWritten);

[DllImport("kernel32.dll", SetLastError = true)]
  public static extern bool WriteProcessMemory(
  IntPtr hProcess,
  IntPtr lpBaseAddress,
  [MarshalAs(UnmanagedType.AsAny)] object lpBuffer,
  int dwSize,
  out IntPtr lpNumberOfBytesWritten);