One more approach you can send using hidden variable.
Take one hidden variable on master page
<input type="hidden" id="textvalue" name="textvalue" />
and you page
<asp:textbox id="TextBox1" xmlns:asp="#unknown">
runat="server"></asp:textbox>
<asp:textbox id="TextBox2" xmlns:asp="#unknown">
runat="server" style="width: 128px"></asp:textbox>
<asp:button id="Button1" runat="server" text="Button" onclick="Button1_Click" onclientclick="storehidden" xmlns:asp="#unknown" />
<script type="text/javascript">
function storehidden() {
document.getElementById('textvalue').value = document.getElementById('TextBox1').value;
}
</script>
in second page you will get the value using Request["textvalue"]
The value also wont able to see in url.