<form action="<?php bloginfo('url'); ?>" method="get">
	<div>
<?php
$taxonomies = array('TAXONOMY NAME');
$args = array('orderby'=>'name','hide_empty'=>true);
$select = get_terms_dropdown($taxonomies, $args);

$select = preg_replace("#<select([^>]*)>#", "<select$1 onchange='return this.form.submit()'>", $select);
echo $select;
?>
	<noscript><div><input type="submit" value="Näytä" /></div></noscript>
	</div></form>
<?php
function get_terms_dropdown($taxonomies, $args){
	$myterms = get_terms($taxonomies, $args);
	$output ="<select name='TAXONOMY SLUG'>";
	foreach($myterms as $term){
		$root_url = get_bloginfo('url');
		$term_taxonomy=$term->taxonomy;
		$term_slug=$term->slug;
		$term_name =$term->name;
		$link = $term_slug;
		$output .="<option value='".$link."'>".$term_name."</option>";
	}
	$output .="</select>";
return $output;
}
?>