Windows Forms

StringBuilder builder = new StringBuilder(500);
uint modTest = GetModuleFileNameEx(Process.GetCurrentProcess().Handle, IntPtr.Zero, builder, 500);
Console.Write(builder.ToString());

[DllImport("psapi.dll")]
static extern uint GetModuleFileNameEx(IntPtr hProcess, IntPtr hModule, [Out] StringBuilder lpFilename, int nSize);

Imports System.Runtime.InteropServices
Imports System.Text

Public Class Form1
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Me.Load
        Text = GetPathOfThisProcessExe()
    End Sub
    Private Function GetPathOfThisProcessExe() As String
        Dim builder As New StringBuilder(500)
        GetModuleFileNameEx(Process.GetCurrentProcess().Handle, IntPtr.Zero, builder, 500)
        Return builder.ToString()
    End Function
    <DllImport("psapi.dll")> _
    Private Shared Function GetModuleFileNameEx( _
    ByVal hProcess As IntPtr, _
    ByVal hModule As IntPtr, _
    <Out()> ByVal lpFilename As StringBuilder, _
    ByVal nSize As Integer) As UInteger
    End Function
End Class