On Enter Button click redirect with querystring as textbox value

put your text box and button in panel with default button

<asp:Panel  DefaultButton="Button1" runat="server">
    <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
    <asp:Button ID="Button1" runat="server" Text="Button" onclick="Button1_Click" /> </asp:Panel >




OR





<script>

     function button_click(objTextBox, objBtnID) {

         if (window.event.keyCode == 13) {

             if (objTextBox.value != "") {

                 document.getElementById(objBtnID).focus();

                 document.getElementById(objBtnID).click();

             }

            

         }

      }

    </script>

<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>

    <asp:Button ID="Button1" runat="server" Text="Button" onclick="Button1_Click" />

Page load:-

this.TextBox1.Attributes.Add("onkeypress", "button_click(this,'" + this.Button1.ClientID + "')");

protected void Button1_Click(object sender, EventArgs e)

    {

        if (!string.IsNullOrEmpty(TextBox1.Text))

        {

            Response.Redirect("Default2.aspx?text=" + TextBox1.Text);

        }

    }