Hi Terence,
Refer below sample.
HTML
MasterPage.aspx
<%@ Master Language="C#" AutoEventWireup="true" CodeFile="MasterPage.master.cs" Inherits="MasterPage" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<asp:ContentPlaceHolder ID="head" runat="server">
</asp:ContentPlaceHolder>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server">
</asp:ContentPlaceHolder>
</div>
</form>
</body>
</html>
CS.aspx
<%@ Page Title="" Language="C#" MasterPageFile="~/MasterPage.master" AutoEventWireup="true"
CodeFile="CS.aspx.cs" Inherits="CS" %>
<asp:Content ID="Content1" ContentPlaceHolderID="head" runat="Server">
<link href="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.2/css/bootstrap.min.css"
rel="stylesheet">
<script src="http://ajax.aspnetcdn.com/ajax/jQuery/jquery-1.8.3.min.js" type="text/javascript"></script>
<script src="http://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.0.3/js/bootstrap.min.js"
type="text/javascript"></script>
<script src="http://oss.maxcdn.com/html5shiv/3.7.2/html5shiv.min.js"></script>
<script src="http://oss.maxcdn.com/respond/1.4.2/respond.min.js"></script>
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="Server">
<div class="modal fade" id="myModal" style="display: none">
<div class="modal-dialog">
<div class="modal-content">
<div class="modal-header">
<button type="button" class="close" data-dismiss="modal" aria-label="Close">
<span aria-hidden="true">×</span></button>
<h4 class="modal-title">
Registration done Successfully</h4>
</div>
<div class="modal-body">
Test Modal
</div>
<div class="modal-footer">
<button type="button" class="btn btn-default" data-dismiss="modal">
Close</button>
<button type="button" class="btn btn-primary">
Save changes</button>
</div>
</div>
</div>
</div>
<asp:Button runat="server" ID="btnShowPopup" Text="Show" CssClass="btn btn-primary"
data-toggle="modal" data-target="#myModal" />
</asp:Content>
Screenshot
