This is too little information.

Please show the code to demonstrate the problem.

There are similar code

package main
import (
    "crypto/tls"
    "fmt"
    "io/ioutil"
    "net/http"
    "net/http/cookiejar"
    "net/url"
    "strings"
)
func init() {
    cfg := &tls.Config{
        InsecureSkipVerify: true,
    }
    http.DefaultClient.Transport = &http.Transport{
        TLSClientConfig: cfg,
    }
}
func httpPostForm() {
    parm := url.Values{}
    parm.Add("username", "***")
    parm.Add("passwd", "***")
    cookieJar, _ := cookiejar.New(nil)
    client := &http.Client{
        Jar: cookieJar,
    }
    req, err := http.NewRequest("POST", "https://www.gjsq.biz/index.php", strings.NewReader(parm.Encode()))
    req.Header.Add("User-Agent", "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/39.0.2171.95 Safari/537.36")
    req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
    resp, err := client.Do(req)
    if err != nil {
        fmt.Printf("%s", err)
    }
    defer resp.Body.Close()
    body, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        fmt.Printf("%s", err)
    }
    fmt.Println(string(body))
}
func main() {
    httpPostForm();
}

It looks like one of the signatories in the path are not known/trusted by Ubuntu (nor my mac as it turns out). This appears to be a common problem with RapidSSL certs.

http://serverfault.com/questions/391487/why-is-my-rapidssl-certificate-chain-is-not-trusted-on-ubuntu

Closing: invalid. Sorry, this isn't a Go bug.

Actually, the real problem is that the server (www.gjsq.biz:443) fails to
send the
complete certificate chain.

A real chain (which is trusted) should look like this:
ww.gjsq.biz 17dec748aea57d1d965a9f3ad80d2e12e100d859 RSA 2048 bits (e
65537) / SHA256withRSA
RapidSSL SHA256 CA - G3 0e34141846e7423d37f20dc0ab06c9bbd843dc24 RSA 2048
bits (e 65537) / SHA256withRSA
GeoTrust Global CA Self-signed de28f4a4ffe5b92fa3c503d1a349a7f9962a8212
RSA 2048 bits (e 65537) / SHA1withRSA

Because GeoTrust Global CA root CA should really be included in all major
OSes,
the problem is not that RapidSSL certificates are not trusted. The server
just failed
to send the crucial intermediate certificate that links from GeoTrust to
RapidSSL.

The conclusion is the same. It's not Go's problem. Perhaps the OP should
contact
that owner of the server and notify them that their web server is
misconfigured.