Get page ID by template

(Requires PHP 5.4+)

function get_page_id_by_template() {
	$args = [
	    'post_type' => 'page',
	    'fields' => 'ids',
	    'nopaging' => true,
	    'meta_key' => '_wp_page_template',
	    'meta_value' => 'page-special.php'
	];
	$pages = get_posts( $args );
	foreach ( $pages as $page ) { 
	    echo $page . '';
	}
}