final String appPackageName = getPackageName();

​

try {

    startActivity(new Intent(Intent.ACTION_VIEW, 

         Uri.parse("market://details?id=" + appPackageName)));

} catch (android.content.ActivityNotFoundException anfe) {

    startActivity(new Intent(Intent.ACTION_VIEW, 

        Uri.parse("https://play.google.com/store/apps/details?id=" + appPackageName)));

}