You can render the TextBox control to as password type by setting its TextMode property to Password.
TextBoxAsPassword.aspx
<%@ Page Language=”vb” AutoEventWireup=”false” CodeBehind=”TextBoxAsPassword.aspx.vb”
Inherits=”TextBoxSamplesVB.TextBoxAsPassword” %>
<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN” “https://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd”>
<html xmlns=”https://www.w3.org/1999/xhtml”>
<head runat=”server”>
<title>Password type TextBox</title>
</head>
<body>
<form id=”form1″ runat=”server”>
<div>
<asp:TextBox ID=”tbPassword” runat=”server” TextMode=”Password”></asp:TextBox>
</div>
</form>
</body>
</html>