<?php 
$seminar=array
(
    0 => 3,
     1 => 8,
    2 => 9,
    3 => 13,
    4 => 14,
    5 => 15
)
;
if (is_array($seminar)) {
foreach ($seminar as $sem_id){
    $sem_id_list .= "$sem_id";
    echo "$sem_id<br />";
}
}
?>

3<br />8<br />9<br />13<br />14<br />15<br />