C# Definition:

[StructLayout(LayoutKind.Sequential)] struct GUID

        {
          public short a;
          public short b;
          public short c;
          [MarshalAs(UnmanagedType.ByValArray, SizeConst=7)]
          public byte[] d;
        }

VB Definition:

<StructLayout(LayoutKind.Sequential)> _
Private Structure GUID
   Dim a As Integer
   Dim b As Short
   Dim c As Short
   <MarshalAs(UnmanagedType.ByValArray, SizeConst:=7)> _
   Dim d() As Byte
End Structure

User-Defined Field Types:

None.

Notes:

You should use System.Guid instead.