Código HTML:
<script>
function show_hide() {
if(document.getElementById('check_sh').checked) {
document.getElementById('select_sh').style.display = "block";
} else {
document.getElementById('select_sh').style.display = "none";
}
}
</script>
<form>
<input type="checkbox" id="check_sh" onclick="show_hide() " />
<select name="sele" id="select_sh">
<option>--</option>
</select>
</form> Te debe funcionar...
:)