JSFiddle - React, Tailwind, and code Playground

HTML

<select name="criteria[]">
    <option value="null" disabled selected>- select -</option>
    <option value="a">a</option>
    <option value="b">b</option>
    <option value="c">c</option>
</select>
<select name="criteria[]">
    <option value="null" disabled selected>- select -</option>
    <option value="a">a</option>
    <option value="b">b</option>
    <option value="c">c</option>
</select>

<select name="criteria[]">
    <option value="null" disabled selected>- select -</option>
    <option value="a">a</option>
    <option value="b">b</option>
    <option value="c">c</option>
</select>

<button id='btnGetVal' type='button'>Get Values</button>

JavaScript

$(function(){
    
    var array = [];
    $('#btnGetVal').on('click', function(){
        $('select[name="criteria[]"]').each(function(){
            console.log($(this).val());
            array.push($(this).val());
        });        
        
        console.log(array);
        
        $.ajax({
            type: 'post',
             url: 'yourfile.php',
            data: {values:array},
            success: function(d){
                // do something on success
            }
        });
        
    });
    
    
});